Semiconductor device and manufacturing method thereof

ABSTRACT

The present invention has an object to provide an active-matrix liquid crystal display device that realizes the improvement in productivity as well as in yield. In the present invention, a laminate film comprising the conductive film comprising metallic material and the second amorphous semiconductor film containing an impurity element of one conductivity type and the amorphous semiconductor film is selectively etched with the same etching gas to form a side edge of the first amorphous semiconductor film  1001  into a taper shape. Thereby, a coverage problem of a pixel electrode  1003  can be solved and an inverse stagger type TFT can be completed with three photomask. Selected figure is FIG.  15.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the invention

[0002] The present invention relates to a semiconductor device includinga semiconductor circuit constituted of a thin-film transistor(hereinafter, abbreviated as a TFT) and a manufacturing method thereof.More particularly, the present invention relates to an electro-opticaldevice as represented by a liquid crystal display panel and anelectronic device including such an electro-optical device as aconstituent.

[0003] Throughout the specification, the term “semiconductor device”indicates all devices that utilize the semiconductor characteristics tofunction; electro-optical devices (hereinafter, referred to as displaydevices), semiconductor circuits and electronic devices are all includedin the category of the semiconductor devices.

[0004] 2. Description of the Related Art

[0005] Recently, there has been developed a technique for manufacturinga TFT by using a thin semiconductor film (with a thickness of abouthundreds to thousands of nm) formed on a substrate which has aninsulating surface. The TFT is widely applied to semiconductor devicessuch as an integrated circuit (IC) or an electro-optical device, and isurgently expected to be developed as, in particular, a switching elementfor a display device or the like.

[0006] An active-matrix liquid crystal display device is frequently usedas a semiconductor device because images with high definition can beobtained as compared with a passive liquid crystal display device. Theactive-matrix liquid crystal display device includes: a gate wiring; asource wiring; a TFT in a pixel portion, which is provided at the crosspoint of the gate wiring and the source wiring; and a pixel electrodeconnected to the TFT in the pixel portion.

[0007] An amorphous silicon film is used as an amorphous semiconductorfilm for a conventional TFT because the amorphous silicon film can beformed on a large substrate at a low temperature of 300° C. or less. Aninverse-stagger type TFT having a channel formation region formed of anamorphous semiconductor film is widely used.

[0008] Conventionally, a TFT is formed on a substrate by using five ormore photomasks through a photolithography technique in an active-matrixelectric device. The reduction of the number of manufacturing steps isbelieved to be effective to improve the productivity and the yield.

[0009] For the reduction of the number of manufacturing steps, it isnecessary to reduce the number of photomasks used in the manufacture ofthe TFT. With the use of one photomask, the steps of resist application,prebaking, exposure, development, postbaking and the like, the precedingand following steps of forming a coating film, etching and the like,and, furthermore, the step of resist removal, washing and drying, areinevitably added to complicate the manufacture of the TFT.

SUMMARY OF THE INVENTION

[0010] The present invention has been made to cope with the aboveproblem, and has an object of reducing the number of photomasks used formanufacturing a TFT in an active-matrix liquid crystal display device soas to realize the improvement in productivity and yield.

[0011] Moreover, the present invention has another object of solving aproblem of poor coverage of a pixel electrode at the end of a pixel TFT,which generally occurs with the reduction of the number of photomasks,and of providing a structure for preventing an insulating film frombeing etched during the etching of an amorphous semiconductor film and amanufacturing method thereof.

[0012] The present invention is characterized in that the manufacturingsteps from the step of forming a conductive film for forming a gatewiring and a capacitance wiring and a terminal electrode to the step offorming a pixel electrode are carried out with three photomasks so as tosolve the problem of poor coverage of a pixel electrode and to preventan insulating film from being etched during the etching of an amorphoussemiconductor film.

[0013] The three photomasks are respectively characterized as follows:

[0014] the first photomask is for forming a conductive film; the secondphotomask is for forming a first amorphous semiconductor film and asecond amorphous semiconductor film containing an impurity element withone conductivity type (n-type or p-type); and

[0015] the third photomask is for forming a pixel electrode, a sourceregion, a drain region, a source electrode and a drain electrode, andfor channel etching.

[0016] According to a constitution of a manufacturing method disclosedin the present specification, a method of manufacturing a semiconductordevice comprising:

[0017] a first step of forming a gate wiring over an insulating surface;

[0018] a second step of forming an insulating film covering saidinsulating surface and said gate wiring;

[0019] a third step of forming a first amorphous semiconductor film overthe insulating film;

[0020] a fourth step of forming a second amorphous semiconductor filmcontaining an impurity element of one conductivity type over the firstamorphous semiconductor film;

[0021] a fifth step of forming a conductive film comprising a metallicmaterial over the second amorphous semiconductor film;

[0022] a sixth step of forming an side edge of the first amorphoussemiconductor film into a taper shape by etching the first amorphoussemiconductor film and the second amorphous semiconductor film and theconductive film;

[0023] a seventh step of forming a transparent conductive film over theconductive film;

[0024] an eighth step of etching a part of the first amorphoussemiconductor film and the second amorphous semiconductor film and theconductive film and the transparent conductive film to expose a part ofthe first amorphous semiconductor film and to form a pixel electrodeformed from the transparent conductive film, a source wiring formed fromthe conductive film, source region and drain region formed from thesecond amorphous semiconductor film.

[0025] In the sixth step, the conductive film and the second amorphoussemiconductor film and the first amorphous semiconductor film are etchedby chlorine group gas.

[0026] A TFT manufactured by utilizing the present invention is shown inFIG. 15. In the present invention, the ends of a first amorphoussemiconductor film 1001 are tapered so as to improve the coverage. Inorder to taper the ends of the first amorphous semiconductor film 1001,by etching the first amorphous semiconductor film 1001 using an etchinggas of chlorine group while etching the metallic layer 1002 a to formsource electrode and drain electrode (and the second amorphoussemiconductor film 1002 b for forming source region and drain region),only side edges of the first amorphous semiconductor film 1001 can beformed into taper shape. Ultimately, an inverse-stagger TFT in whichcoverage defect of a pixel electrode 1003 has been solved can bemanufactured with three photomasks in total. Moreover, when theamorphous semiconductor film is to be etched, it is possible to preventan insulating film 1004 from etching in the vicinity of the ends of thefirst amorphous semiconductor film 1001.

[0027] In this way, in the present invention, a multilayer film (metalfilm, second amorphous semiconductor film and first amorphoussemiconductor film) comprising a plurality of different materials isetched at a time using the same etching gas (chlorine group) with asecond photomask to improve throughput.

[0028] Herein, a tapered shape angle (taper angle) of the firstamorphous semiconductor film 1001 is defined as an angle formed by thesurface of a substrate and an inclined portion of the end of the firstamorphous semiconductor film (FIG. 21B). As shown in FIG. 21A, a taperangle of the end of the first amorphous semiconductor film can becontrolled to fall within the range of 5 to 45 degrees by appropriatelyselecting the etching conditions.

[0029] A chlorine type etching gas is used as an etching gas forcarrying out the present invention. For example, a gas selected from thegroup consisting of Cl₂, BCl₃, HCl and SiCl₄, or a mixed gas of aplurality of gases selected from the above group, can be used as anetching gas.

[0030] Because the chlorine type gas has little difference betweenetching rate to the metal layer 1002 a and the etching rate to thesecond amorphous semiconductor film 1002 b, their side edges are almostmade aligned. A chlorine type etching gas has different etching ratesfor the first amorphous semiconductor film and a second amorphoussemiconductor film containing an impurity element with one conductivitytype (n-type or p-type). Since the etching rate for the second amorphoussemiconductor is higher than that for the first amorphous semiconductorfilm, the ends of the first amorphous semiconductor film can be formedin a tapered shape.

[0031] In one constitution of the present invention shown in FIG. 15, asemiconductor device comprises a gate wiring over an insulating surface,an insulating film over the gate wiring, a first amorphous semiconductorfilm over the insulating film, a source region and a drain regionprovided in a second amorphous semiconductor film containing an impurityelement of one conductivity type over the first amorphous semiconductorfilm, a source wiring or electrode over the source region or the drainregion, and a pixel electrode overlapping and in contact with a part ofthe electrode, wherein a side edge of the first amorphous semiconductorfilm is tapered.

[0032] In FIG. 15, the side edge of the second amorphous semiconductorfilm 1002 b (source region or drain region) containing an impurityelement of one conductivity type (n-type or p-type) is formed almostperpendicularly to the substrate, that is, in alignment with the sideedge of the metal layer 1002 a (source electrode and drain electrode).However, side edge of the second amorphous semiconductor film 1002 bcontaining the impurity element of one conductivity type (n-type orp-type) or side edge of the metal layer 1002 a may be etched into ataper shape.

[0033] In other constitution of the present invention, a semiconductordevice comprises a gate wiring over an insulating surface, an insulatingfilm over the gate wiring, a first semiconductor film over theinsulating film, a source region and a drain region provided in a secondamorphous semiconductor film containing an impurity element of oneconductivity type over the first amorphous semiconductor film, a sourcewiring or electrode over the source region and the drain region, and apixel electrode overlapping with and being in contact with a part of theelectrode, wherein a side edge of the first amorphous semiconductor filmand a side edge of the second amorphous semiconductor film are tapered.

[0034] It is to be noted that in the case where the side edge of thesecond amorphous semiconductor film 1002 b or the side edge of the metallayer 1002 a are tapered, they have a taper angle larger than that ofthe first amorphous semiconductor film.

[0035] Further, a dry etching apparatus used in the present inventionmay be an etching apparatus of RIE or an etching apparatus of ICP. It isto be noted that because a taper angle can be controlled by controllingelectric power, the etching apparatus of ICP is preferable.

[0036] An etching experiment was conducted. After an insulating film(silicon oxide film) and a first amorphous semiconductor film (amorphoussilicon film) and a second amorphous semiconductor film (phosphorusdoped silicon film) and Al-Si film (aluminum film containing 2 wt %silicon) were laminated in order, they were selectively covered with aresist and they were etched using a mixture gas of Cl₂ and BCl₃ in fact.The cross-sectional view after that was observed and is shown in FIG.19. In FIG. 19, SEM (Scanning Electron Microscope) photograph is shownand its magnification is fifty thousands times. By conducting theetching with the mixture gas of Cl₂ and BCl₃, the Al—Si film and thesecond amorphous semiconductor film and the first amorphoussemiconductor film can be etched at the same time, and further, only theside edge of the first amorphous semiconductor film can be tapered.

[0037] Further, it is possible to use other metal materials in place ofthe Al-Si film. In that case, it is necessary to select etchingcondition, typically etching gas. For example, in the case where Ta film(tantalum film) is used as the metal film 1002 a, by etching the firstamorphous semiconductor film (amorphous silicon film) and the secondamorphous semiconductor film (phosphorus doped silicon) and the Ta film,only the first amorphous semiconductor film can be tapered.

[0038] Further, in the case where a multi-layer of Tan and Ta is used asthe metal film 1002 a, by using a mixture gas of Cl₂ (gas flow rate of40 sccm) and CF₄ (gas flow rate of 40 sccm as etching gas, the firstamorphous semiconductor film (amorphous silicon film) and the secondamorphous semiconductor film (phosphorus doped silicon film) and themulti-layer film of Tan and Ta are etched and only the first amorphoussemiconductor film can be tapered.

[0039] Further, in the case where W (tungsten) film is used as the metallayer 1002 a, by using a mixture gas of Cl₂ (gas flow rate of 25 sccm)and CF₄ (gas flow rate of 25 sccm) and O₂ (gas flow rate of 10 sccm) ora mixture gas of Cl₂ (gas flow rate of 12 sccm) and SF₆ (gas flow rateof 6 sccm) and O₂ (gas flow rate of 12 sccm) as an etching gas, the firsamorphous semiconductor film (amorphous silicon film) and the secondamorphous semiconductor film (phosphorus doped silicon film) and the Wfilm are etched, and the first amorphous semiconductor film can betapered similarly.

[0040] Further, in the case where Ti (titanium) film is used as themetal layer 1002 a, by using a mixture gas of Cl₂ and BCl₃ as an etchinggas, the first amorphous semiconductor film (amorphous silicon film) andthe second amorphous semiconductor film (phosphorus doped silicon film)and Ti film are etched, and only the first amorphous semiconductor filmcan be tapered.

[0041] Further, in FIG. 15, when formed into an island shape by etchingusing the second photomask, the side edge of the first amorphoussemiconductor film is tapered, as illustrated above. However, as shownin FIG. 23, the present invention can be applied to a step (channeletching) of removing a part of the first amorphous semiconductor film2001 overlapping with the gate electrode 2000 through an insulatingfilm. By using a third photomask and using an etching gas of chlorinetype similarly, the metal layer 2002 a and the second amorphoussemiconductor film 2002 b and the first amorphous semiconductor film2001 are etched and only the first amorphous semiconductor film 2001 canbe tapered so that a protective film (passivation film) is formed withfavorable coverage at a later step. It is to be noted that referencenumeral 2003 designates a pixel electrode and the reference numeral 2004designates a gate insulating film.

[0042] Further, in the eighth step of the constitution of the abovemanufacturing method, a part of the first amorphous semiconductor filmand the conductive film and the second amorphous semiconductor film areetched with a chlorine type gas.

[0043] Further, according to the constitution shown in FIG. 23 accordingto one of the present invention, a semiconductor device comprises a gatewiring over an insulating surface, a gate insulating film over the gatewiring, an amorphous semiconductor film over the gate insulating film, asource region and a drain region over the amorphous semiconductor film,a source wiring or electrode over the source region and the drainregion, and a pixel electrode overlapping with and in contact with apart of the electrode wherein a region of the amorphous semiconductorfilm overlapping with the gate wiring with the gate insulating filmtherebetween and not overlapping with the source region and the drainregion has a thickness thinner than the other region and is tapered tobecome thin toward the center thereof.

[0044] Further, in the above constitution, the region having the tapershape has an angle in the range of 5° to 45°.

[0045] Further, in the above constitution, the side edge of the firstamorphous semiconductor film may be tapered with an angle in the rangeof 5° to 45°.

[0046] On the other hand, as a comparative example, FIG. 16 shows a TFTincluding a first amorphous semiconductor film and a second amorphoussemiconductor film, each having the ends that are etched to beperpendicular to the substrate. The amorphous semiconductor films 1005and 1006 b are etched separately from the etching of the metal layer1006 a. After the metal layer 1006 a is selectively wet etched, a firstamorphous semiconductor film 1005 and a second amorphous semiconductorfilm 1006 containing an impurity element with one conductivity type(n-type or p-type) of the TFT are dry etched with a mixed gas of CF₄ andO₂ using the metal layer as a mask. The first amorphous semiconductorfilm 1005 and the second amorphous semiconductor film 1006 containing animpurity element with one conductivity type (n-type or p-type) aresimultaneously etched. As a result, the shapes of the ends of the firstamorphous semiconductor film 1005 and the second amorphous semiconductorfilm 1006 containing an impurity element with one conductivity type(n-type or p-type) is formed to be perpendicular to the substrate in thealmost same shape as each other as shown in FIG. 16. Then, a pixelelectrode 1007 is formed on these films 1005 and 1006. In the respectiveetchings in the comparative example, a side etching (an undercut) isproduced so that when a film is formed later, there is a fear that thefilm might be cut at a step.

[0047] In the above-described structure shown in FIG. 16, poor coverageoccurs at the ends of the first amorphous semiconductor film 1005 andthe second amorphous semiconductor film 1006 containing an impurityelement with one conductivity type (n-type or p-type) and the metallayer 1006 a. The poor coverage occurs to such a degree that the pixelelectrode 1007 cannot be formed in a normal state due to a poor etchingor due to a step shape of the three layers.

[0048] During the etching for manufacturing the above shape shown inFIG. 16, an insulating film 1008 in the vicinity of the ends of thefirst amorphous semiconductor film 1005 is also etched to generate avariation of the insulating film in thickness.

[0049] The other structure of the present invention, which is differentfrom the above-described structure, will be described below. In thepresent invention, the manufacturing steps from the formation of aconductive film to the formation of a pixel electrode are carried outwith three photomasks so as to solve the problem of poor coverage of apixel electrode.

[0050] The three photomasks are respectively characterized as follows:

[0051] the first photomask is for forming a conductive film;

[0052] the second photomask is for forming an insulating film, a firstamorphous semiconductor film, and a second amorphous semiconductor filmcontaining an impurity element with one conductivity type (n-type orp-type); and

[0053] the third photomask is for forming a pixel electrode, a sourceregion, a drain region, a source electrode and a drain electrode, andfor channel etching.

[0054] According to other constitution of manufacturing method shown inthe present specification, a method for manufacturing a semiconductordevice comprises:

[0055] a first step of forming a gate wiring over an insulating surface;

[0056] a second step of forming an insulating film covering theinsulating surface and the gate wiring;

[0057] a third step of forming a first amorphous semiconductor film overthe insulating film;

[0058] a fourth step of forming a second amorphous semiconductor filmcontaining an impurity element of one conductivity type over the firstamorphous semiconductor film;

[0059] a fifth step of forming a conductive film comprising a metallicmaterial over the second amorphous semiconductor film;

[0060] a sixth step of etching the insulating film and the firstamorphous semiconductor film and the second amorphous semiconductor filmand the conductive film to taper a side edge of the first amorphoussemiconductor film;

[0061] a seventh step of forming a transparent conductive film over theconductive film; and

[0062] an eighth step of etching a part of the first amorphoussemiconductor film and the transparent conductive film and theconductive film and the second amorphous semiconductor film to expose apart of the first amorphous semiconductor film and to form a pixelelectrode from the transparent conductive film and to form a sourcewiring from the conductive film and to form a source region and a drainregion from the second amorphous semiconductor film.

[0063] A TFT manufactured by utilizing the present invention is shown inFIG. 17. According to the present invention, the ends of a firstamorphous semiconductor film 1801 are tapered so as to improve thecoverage. In order to taper the ends of the first amorphoussemiconductor film 1801, an inverse-stagger TFT is manufactured withthree photomasks by using a chlorine type etching gas. As a result, theends of the first amorphous semiconductor film 1801 can be manufacturedto have a tapered shape, thereby solving the problem of poor coverage ofa pixel electrode 1803.

[0064] Herein, a tapered shape angle (taper angle) of the firstamorphous semiconductor film 1801 is defined as an angle formed by thesurface of a substrate and an inclined portion of the end of the firstamorphous semiconductor film 1801 (FIG. 22B). As shown in FIG. 22A, ataper angle of the end of the first amorphous semiconductor film can becontrolled to fall within the range of 5 to 45 degrees by appropriatelyselecting the etching conditions.

[0065] A chlorine type etching gas is used as an etching gas forcarrying out the present invention. For example, a gas selected from thegroup consisting of Cl₂, BCl₃, HCl and SiCl₄, or a mixed gas of aplurality of gases selected from the above group, can be used as anetching gas.

[0066] Because a chlorine type gas has an etching rate to the metallayer 1802 a and an etching rate to the second amorphous semiconductorfilm with a little difference, their side edges are almost aligned witheach other. However, a chlorine type gas has different etching rates forthe first amorphous semiconductor film and a second amorphoussemiconductor film containing an impurity element with one conductivitytype (n-type or p-type). Since the etching rate for the second amorphoussemiconductor film containing an impurity element with one conductivitytype (n-type or p-type) is higher than that for the first amorphoussemiconductor film, the ends of the first amorphous semiconductor filmcan be formed in a tapered shape.

[0067] According to the constitution of one of the present inventionshown in FIG. 17, a semiconductor device comprises a gate wiring over aninsulating surface, an insulating film over the gate wiring, a firstamorphous semiconductor film over the insulating film, a source regionand a drain region provided in a second amorphous semiconductor filmcontaining an impurity element of one conductivity type over the firstamorphous semiconductor film, a source wiring or electrode over thesource region or the drain region, and a pixel electrode overlappingwith and in contact with a part of the electrode, wherein only a sideedge of the first amorphous semiconductor film is tapered and is alignedwith a side edge of the insulating film, and the side edge of theinsulating film is not aligned with the source wiring or electrode.

[0068] In FIG. 17, the ends of a metal layer 1802 a and a secondamorphous semiconductor film 1802 containing an impurity element withone conductivity type (n-type or p-type) are formed so as to beperpendicular to the substrate. However, the ends of a metal layer 1802a and a second amorphous semiconductor film 1802 containing an impurityelement with one conductivity type (n-type or p-type) may alternativelybe formed in a tapered shape.

[0069] An experiment of the etching was carried out. An insulating filmand a first amorphous semiconductor film and a second amorphoussemiconductor film and an Al—Si film (aluminum film containing 2 wt %silicon) are laminated over a substrate in order. Thereafter, they areselectively covered with a photoresist and actually etched using a mixedgas of Cl₂ and BCl₃. A resultant cross-sectional view was observed andis shown in FIG. 20. FIG. 20 is an SEM (scanning electron microscope)photograph taken at a magnifying power of 50000. By etching with amixture gas of Cl₂ and BCl₃, the Al—Si film and the second amorphoussemiconductor film and the first amorphous semiconductor film can beetched at the same time so that only a side edge of the first amorphoussemiconductor film can be tapered. Further, in FIG. 20, the insulatingfilm is removed using the first amorphous semiconductor film as a mask.

[0070] Further, in FIG. 17, when formed into an island shape by etchingusing the second photomask, the side edge of the first amorphoussemiconductor film is tapered. However, in a channel etch type TFT, thepresent invention can be applied a step (channel etching) of removing apart of the first amorphous semiconductor film overlapping with the gateelectrode through the insulating layer. By using a third photomask andan etching gas of chlorine type similarly, the metal layer and thesecond amorphous semiconductor film and the first amorphoussemiconductor film and the insulating film are etched, and only thefirst amorphous semiconductor film can be tapered so that in the casewhere a protective film (passivation film) is formed at a later step, afavorable coverage can be obtained.

[0071] On the other hand, as a comparative example, FIG. 18 shows a TFTincluding a first amorphous semiconductor film and a second amorphoussemiconductor film, each having the ends that are etched to beperpendicular to the substrate. Etching of the metal layer 1902 a andetching of the amorphous semiconductor films 1901 and 1902 b areconducted separately from each other. After the metal layer 1902 a isselectively etched, a first amorphous semiconductor film 1901 and asecond amorphous semiconductor film 1902 containing an impurity elementwith one conductivity type (n-type or p-type) of the TFT are etched witha mixed gas of CF₄ and O₂. The first amorphous semiconductor film 1901and the second amorphous semiconductor film 1902 containing an impurityelement with one conductivity type (n-type or p-type) are simultaneouslyetched. As a result, the ends of the first amorphous semiconductor film1901 and the second amorphous semiconductor film 1902 containing animpurity element with one conductivity type (n-type or p-type) areformed to be perpendicular to the substrate as shown in FIG. 18. Then, apixel electrode 1903 is formed on these films.

[0072] In the above-described structure, poor coverage occurs at theends of the first amorphous semiconductor film 1901 and the secondamorphous semiconductor film 1902 containing an impurity element withone conductivity type (n-type or p-type) and the metal film 1902 a andthe insulating film 1904. The poor coverage occurs to such a degree thatthe pixel electrode 1903 can not be formed in a normal state due to thethickness of the four films.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] In the accompanying drawings:

[0074]FIG. 1 is a top plan view showing a pixel;

[0075]FIGS. 2A to 2C are diagrams showing the steps of manufacturing asemiconductor device;

[0076]FIGS. 3A to 3C are diagrams showing the steps of manufacturing thesemiconductor device;

[0077]FIGS. 4A and 4B are diagrams showing the steps of manufacturingthe semiconductor device;

[0078]FIGS. 5A to 5C are diagrams showing the steps of manufacturing thesemiconductor device;

[0079]FIGS. 6A to 6C are diagrams showing the steps of manufacturing thesemiconductor device;

[0080]FIGS. 7A to 7C are diagrams showing the steps of manufacturing thesemiconductor device;

[0081]FIG. 8 is a top plan view showing a pixel in Embodiment 3 of thepresent invention;

[0082]FIGS. 9A to 9C are diagrams showing the steps of manufacturing thesemiconductor device;

[0083]FIGS. 10A to 10C are diagrams showing the steps of manufacturingthe semiconductor device;

[0084]FIGS. 11A to 11C are diagrams showing the steps of manufacturingthe semiconductor device;

[0085]FIGS. 12A and 12B are diagrams showing the steps of manufacturingthe semiconductor device;

[0086]FIGS. 13A and 13B are diagrams showing the steps of manufacturingthe semiconductor device;

[0087]FIGS. 14A to 14D are diagrams illustrating examples of apparatusesutilizing the semiconductor device;

[0088]FIG. 15 is a cross-sectional view showing a thin-film transistormanufactured by using the present invention;

[0089]FIG. 16 is a cross-sectional view showing a thin film transistor(comparative example);

[0090]FIG. 17 is a cross-sectional view showing another thin-filmtransistor according to the present invention;

[0091]FIG. 18 is a cross-sectional view showing another thin filmtransistor (comparative example);

[0092]FIG. 19 is a cross-sectional SEM showing a thin film transistoraccording to the present invention;

[0093]FIG. 20 is a cross-sectional SEM showing another thin filmtransistor according to the present invention;

[0094]FIGS. 21A and 21B are diagrams for defining the taper angle;

[0095]FIGS. 22A and 22B are another diagrams for defining the taperangle; and

[0096]FIG. 23 is a cross-sectional view showing a thin film transistoraccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0097] Hereinafter, a semiconductor device manufactured by carrying outthe present invention will be described.

EMBODIMENT MODE 1

[0098] First, a conductive film is formed on the entire surface of asubstrate. The conductive film is formed into a desired shape through afirst photolithography step. As a material of the conductive film, anelement selected from W, WSi_(x), Al, Ti, Mo, Cu, Ta, Cr, Ni, and Mo, afilm containing as a main component an alloy material or compoundmaterial containing the element as a main component, or a multi-layerfilm thereof can be enumerated. Later, the conductive film is etched tobecome a gate electrode or a gate wiring or a retention capacitancewiring.

[0099] Next, an insulating film is formed on the entire surface of theconductive film. Later, the insulating film functions as a gateinsulating film. A first amorphous semiconductor film and a secondamorphous semiconductor film containing an impurity element with oneconductivity type (n-type or p-type) and a conductive film comprising ametallic material (a metallic material containing Al, Ti, Mo, Cu, Ta,Cr, Ni or Mo as a main component) are formed on the insulating film.Here, a conductive film containing Al as a main component is formed.

[0100] Then, an unnecessary portion of the layered film formed of thefirst amorphous semiconductor film and the second amorphoussemiconductor film containing an impurity element with one conductivitytype (n-type or p-type) and the conductive film comprising metallicmaterial is removed by etching through a second photolithography step.Here, without changing the etching gas, the first amorphoussemiconductor film and the second amorphous semiconductor film and theconductive film are etched. The etching is conducted using a chlorinetype gas for example a mixed gas of Cl₂ and BCl₃ as an etching gas sothat the ends of the conductive film comprising metallic material (Al)and the second amorphous semiconductor film containing an impurityelement with one conductivity type (n-type or p-type) are etchedperpendicularly to the substrate while the ends of the first amorphoussemiconductor film are tapered. Note that the ends of the secondamorphous semiconductor film containing an impurity element with oneconductivity type (n-type or p-type) may also be tapered.

[0101] Here, because a conductive material containing Al as a maincomponent as the conductive film to become a source electrode or a drainelectrode later, etching is conducted using a mixture gas of Cl₂ andBCl₃ as an etching gas. However, not limited to that. When a materialcontaining Ti is used, the side edge of the first amorphoussemiconductor film can be tapered using the same mixture gas. Further,when a conductive material containing Ta as a main component is used forthe conductive film, the side edge of the first amorphous semiconductorfilm can be tapered by using Cl₂ gas or a mixture gas of Cl₂ gas and CF₄gas. Further, when a conductive material containing W as a maincomponent is used for the conductive film, the side edge of the firstamorphous semiconductor film can be tapered by using a mixture gas ofCl₂ gas and CF₄ gas and O₂ gas or a mixture gas of Cl₂ gas and SF₄ gasand O₂ gas.

[0102] Next, after removal of a second resist mask, another resist maskis formed by using a shadow mask so as to selectively remove theinsulating film covering a pad portion of a terminal portion.

[0103] Next, a conductive film comprising a transparent conductive filmis formed over the entire surface. As the transparent conductive film,ITO (indium oxide- tin oxide alloy) and an indium oxide—zinc oxide alloy(In₂O₃-ZnO) and zinc oxide (ZnO) are enumerated.

[0104] Next, a part of the first amorphous semiconductor film and thetransparent conductive film and the conductive film comprising metallicmaterial and the second amorphous semiconductor film containing animpurity element with one conductivity type (n-type or p-type) areremoved through a third photolithography step to form a source regionand a drain region provided in the second amorphous semiconductor filmand to simultaneously form a source wiring from the conductive filmcomprising metallic material and form a pixel electrode from thetransparent conductive film.

[0105] Further, when etching is conducted by using a chlorine gas forexample a mixture gas of Cl2 and BCl3 as an etching gas in the thirdphotolithography step, a part to become a channel formation region canbe tapered as shown in FIG. 23.

[0106] As described above, through three photolithography steps, asemiconductor device including a pixel TFT which has the first amorphoussemiconductor film with the tapered ends, the source wiring comprisingmetallic material, a storage capacitor, and the terminal portion can bemanufactured.

EMBODIMENT MODE 2

[0107] First, a conductive film is formed on the entire surface of asubstrate. The conductive film is formed into a desired shape through afirst photolithography step. Later, the conducive film is etched to forma gate electrode or a gate wiring or a storage capacitance wiring.

[0108] Next, an insulating film is formed on the entire surface of theconductive film. Later, the insulating film functions as a gateinsulating film. A first amorphous semiconductor film and a secondamorphous semiconductor film containing an impurity element with oneconductivity type (n-type or p-type) and a conductive film comprisingmetallic material (metallic material containing Al, Ti, Mo, Cu, Ta, Cr,Ni or Mo as a main component) are deposited on the insulating film.

[0109] Then, an unnecessary portion of the layered film formed of thefirst amorphous semiconductor film and the second amorphoussemiconductor film containing an impurity element with one conductivitytype (n-type or p-type) and the conductive film comprising metallicmaterial is removed by etching through a second photolithography step.Here, the first amorphous semiconductor film and the second amorphoussemiconductor film and the conductive film are etched without changingthe etching gas. The etching is conducted using a chlorine type gas forexample a mixed gas of Cl₂ and BCl₃ as an etching gas so that the endsof the conductive film comprising metallic material and the secondamorphous semiconductor film containing an impurity element with oneconductivity type (n-type or p-type) are formed to be perpendicular tothe substrate while the ends of the first amorphous semiconductor filmare tapered. Note that the ends of the second amorphous semiconductorfilm containing an impurity element with one conductivity type (n-typeor p-type) may also be tapered.

[0110] Next, an unnecessary portion of the insulating film is removed byetching with continuous use of a second photomask which is used foretching the first amorphous semiconductor film and the second amorphoussemiconductor film containing an impurity element with one conductivitytype (n-type or p-type).

[0111] Next, a conductive film of a transparent conductive film isformed on the entire surface. As the transparent conductive film, ITO(indium oxide—tin oxide alloy) and indium oxide—zinc oxide alloy(In2O3-ZnO) and zinc oxide (ZnO) are enumerated.

[0112] Thereafter, a part of the first amorphous semiconductor film andthe transparent conductive film and the conductive film comprisingmetallic material and the second amorphous semiconductor film containingan impurity element with one conductivity type (n-type or p-type) isremoved through a third photolithography step to form a source regionand a drain region of a gate electrode while forming a source wiringfrom the conductive film comprising metallic material and forming apixel electrode from the transparent conductive film.

[0113] As described above, through three photolithography steps, asemiconductor display device including a pixel TFT which has the firstamorphous semiconductor film with the tapered ends, the source wiring, astorage capacitor, and a terminal portion can be manufactured.

[0114] The present invention with the above-described structures will bedescribed further in detail in the following Embodiments.

EMBODIMENTS Embodiment 1

[0115] Embodiment 1 of the present invention will be described withreference to FIGS. 1 to 4B. In Embodiment 1, a manufacturing method of aliquid crystal display device is described. A method of manufacturing aninverse-stagger TFT in a pixel portion on a substrate and manufacturinga storage capacitor to be connected to the TFT will be described indetail in the order of the manufacturing steps. In FIGS. 2A to 4B, aterminal portion, which is provided at the end of the substrate so as tobe electrically connected to a wiring of a circuit provided on anothersubstrate, is also illustrated in the steps of manufacturing a TFT. Thecross-sectional views of FIGS. 2A to 4B correspond to the cross sectiontaken along a line AA-A′ in FIG. 1.

[0116] First, a display device is manufactured by using a substrate 200with light transmittance. As the substrate 200, a glass substrate suchas barium borosilicate glass and alumino borosilicate glass, asrepresented by #7059 glass and #1737 glass manufactured by Corning Inc.,can be used. Besides, a light transmitting substrate such as a quartzsubstrate and a plastic substrate can also be used as the substrate 200.

[0117] After forming a conductive film on the entire surface of thesubstrate 200, a first photolithography step is conducted to form aresist mask. An unnecessary portion is removed by etching to form gateelectrodes 202 and 203, a storage capacitor wiring 204, and a terminalportion 201 (FIG. 2A).

[0118] As a material for the electrodes 202 and 203, an element selectedfrom the group consisting of titanium (Ti), tantalum (Ta), tungsten (W),molybdenum (Mo), chromium (Cr) and neodymium (Nd), an alloy containingthe above element as a constituent, or a nitride containing the aboveelement as a constituent, is used. Alternatively, the combination ofplural selected from: an element selected from the group consisting oftitanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium(Cr) and neodymium (Nd); an alloy containing the above element as aconstituent; and a nitride containing the above element as aconstituent, can be deposited as a laminate layer to form the electrodes202 and 203.

[0119] For application to a large screen, it is desirable to form gatewirings 202 and 203 including the gate electrodes, the capacitor wiring204 and a terminal of the terminal portion 201, using a low-resistanceconductive material. Therefore, aluminum (Al), copper (Cu), silver (Ag),gold (Au), platinum (Pt) or the like, or an alloy containing the aboveelement as a constituent can be used as a material. Since aluminum (Al),copper (Cu) and silver (Ag) are disadvantageous in their low thermalresistance, high corrosiveness and the like, however, these elements canbe used in combination with a thermally resistant conductive material.

[0120] Next, an insulating film 207 is formed on the entire surface. Asilicon nitride film is used as the insulating film 207, and is formedto have a thickness of 50 to 200 nm, preferably, 150 nm. Note that thegate insulating film 207 is not limited to the silicon nitride film; aninsulating film such as a silicon oxide film, a silicon nitride oxidefilm or a tantalum oxide film can also be used (FIG. 2B).

[0121] Next, a first amorphous semiconductor film 206 with a thicknessof 50 to 200 nm, preferably, 100 to 150 nm, is formed on the entiresurface of the insulating film 207 through a known method such as aplasma CVD method or a sputtering method. Typically, an amorphoussilicon (a-Si) film is formed to have a thickness of 100 nm. As thefirst amorphous semiconductor film 206, a microcrystalline semiconductorfilm and a compound semiconductor film with an amorphous structure, suchas an amorphous silicon germanium film, or an amorphous silicon carbidefilm can also be used (FIG. 2B).

[0122] Next, a second amorphous semiconductor film 205 containing animpurity element with one conductivity type (n-type or p-type) is formedto have a thickness of 50 to 200 nm. The second semiconductor film 205containing an impurity element with one conductivity type (n-type orp-type) is formed on the entire surface by a known method such as aplasma CVD method or a sputtering method. In Embodiment 1, the secondamorphous semiconductor film 205 containing an n-type impurity elementis formed by using a silicon target to which phosphorus (P) is added.Alternatively, the second amorphous semiconductor film 205 may be formedwith a silicon target by sputtering in an atmosphere containingphosphorus. Further alternatively, the second amorphous semiconductorfilm 205 containing an impurity element that imparts an n-typeconductivity may be formed of a microcrystalline silicon hydride film(FIG. 2B). Further, a conductive film 205 b comprising metallic materialis formed to a thickness of 50 to 200 nm by using sputtering or thelike.

[0123] Then, a second photolithography step is conducted to form aresist mask 208. A first amorphous semiconductor film 209 and a secondamorphous semiconductor film 210 containing an impurity element with oneconductivity type (n-type or p-type) and a conductive film 210 b areformed to have a desired shape by selectively removing the conductivefilm and the first amorphous semiconductor film and the second amorphoussemiconductor film by etching . In Embodiment 1, the first amorphoussemiconductor film 209 and the second amorphous semiconductor film 210containing an impurity element with one conductivity type (n-type orp-type) and the conductive film 210 b are formed by dry etching using amixed gas of Cl₂=40 sccm and BCl₃=40 sccm as an etching gas. As a resultof etching, the ends of the conductive film 210 b the second amorphoussemiconductor film 210 a containing an impurity element with oneconductivity type (n-type or p-type) are perpendicular to the substrate,whereas the ends of the first amorphous semiconductor film 209 aretapered at an angle in the range of 5 to 45 degrees (FIG. 2C).

[0124] The ends of the second amorphous semiconductor film 210containing an impurity element with one conductivity type (n-type orp-type) may be tapered. Although the mixed gas of C1 ₂=40 sccm andBCl₃=40 sccm is used as an etching gas in Embodiment 1, a composition ofthe etching gas is not limited to the above-mentioned composition aslong as a TFT with a shape shown in FIG. 2C is obtained; for example, agas selected from the group consisting of Cl₂, BCl₃, HCl and SiCl₄, or amixed gas of a plurality of gases selected from the above group, can beused as an etching gas.

[0125] Next, after removal of the resist mask 208, another resist maskis formed by using a shadow mask. After the insulating film 207, whichcovers a pad portion of the terminal portion, is selectively removed toform an insulating film 301, the resist mask is removed (FIG. 3A).Instead of using the shadow mask, a resist mask formed by screenprinting may alternatively be used as an etching mask.

[0126] Then, a conductive film 302 of a transparent conductive film isformed on the entire surface (FIG. 3B). The conductive film 302 isformed by sputtering or vacuum evaporation, using indium oxide (In₂O₃)or an alloy of indium oxide and tin oxide (In₂O₃-SnO₂; abbreviated asITO) as a material.

[0127] Next, a third photolithography step is conducted to form a resistmask 403. An unnecessary portion is removed by etching to form a pixelelectrode 405 from the transparent conductive film and to form a sourcewiring 402 and a drain electrode 404 and to expose a part of the firstamorphous semiconductor film (FIG. 4A). The etching treatment of theconductive film comprising the transparent conductive film is conductedin a chlorine type solution. After the pixel electrode 405 is formed,etching gases are appropriately changed to etch the metal layer and thesecond amorphous semiconductor film . It is to be noted that in theabove third photolithography step, an overetching is conducted tocompletely separate the source region and the drain region from eachother, and further a part of the first amorphous semiconductor film isremoved. In the removed region of the first amorphous semiconductorfilm, a channel is formed.

[0128] Further, similarly to the second photolithography step, a part ofthe first amorphous semiconductor film and the metal layer and thesecond amorphous semiconductor film may be etched at a time by using achlorine type gas in the third photolithography step. In that case, theetched region of the first amorphous semiconductor film overlaps withthe gate wiring with a gate insulating film therebetween and does notoverlap with the source region or the drain region. The regionoverlapping with the gate wiring with a gate insulating filmtherebetween in the first amorphous semiconductor film is referred to asa channel formation region (back channel part). Further, the etchedregion in the first amorphous semiconductor film has a taper shape inwhich thickness thereof becomes thinner toward a center of the region.Accordingly, it is possible to manufacture a channel etch type TFThaving a channel formation region free from a step.

[0129] Subsequently, a resist mask 401 is removed. FIG. 4B shows across-sectional view in this state.

[0130] As described above, through three photolithography steps, anactive matrix substrate comprising a source wiring 402 and a pixel TFTof an inverse stagger type and the storage capacitor 408 and theterminal portion 409 can be obtained. With respect to the followingsteps, using the know technique, formation of orientation film andrubbing treatment and sticking of a counter substrate and injection ofliquid crystal and sealing and sticking of FPC are conducted to completea liquid crystal display device of transmission type.

[0131] Further, if necessary, a protective film comprising a siliconnitride film or a silicon oxynitride film may be formed. It is notprovided over a terminal electrode connected with FPC.

[0132] The TFT including an active layer formed of the amorphoussemiconductor film, obtained in Embodiment 1, has a small field-effectmobility, i.e., only about 1 cm²/Vsec. Therefore, a driving circuit forperforming the image display is formed with an IC chip, and is mountedthrough TAB (tape automated bonding) or COG (chip on glass).

[0133] Further, a TFT having a multi-gate structure comprising aplurality of channel formation regions, here a TFT having a double-gatestructure, is shown in Embodiment 1. However, a single gate structuremay be used without limitation.

Embodiment 2

[0134] The semiconductor display device including the channel etch typeTFT in the pixel portion has been described in Embodiment 1, while asemiconductor display device including a channel stop type TFT in thepixel portion will be described in Embodiment 2 with reference to FIGS.5A to 7C.

[0135] First, a semiconductor display device is manufactured by using asubstrate 500 with light transmittance. As the substrate 500, a glasssubstrate such as barium borosilicate glass and alumino borosilicateglass, as represented by #7059 glass and #1737 glass manufactured byCorning Inc., can be used. Besides, a light transmitting substrate suchas a quartz substrate and a plastic substrate can also be used as thesubstrate 500.

[0136] After forming a conductive film on the entire surface of thesubstrate 500, a first photolithography step is conducted to form aresist mask. An unnecessary portion is removed by etching to form gateelectrodes 502 and 503, a storage capacitor wiring 504, and a terminalportion 501 (FIG. 5A).

[0137] As a material for the electrodes 502 and 503, an element selectedfrom the group consisting of titanium (Ti), tantalum (Ta), tungsten (W),molybdenum (Mo), chromium (Cr) and neodymium (Nd), an alloy containingthe above element as a constituent, or a nitride containing the aboveelement as a constituent, is used. Alternatively, the combination ofplural selected from: an element selected from the group consisting oftitanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium(Cr) and neodymium (Nd); an alloy containing the above element as aconstituent; and a nitride containing the above element as aconstituent, can be deposited as a laminate layer to form the electrodes502 and 503.

[0138] For application to a large screen, it is desirable to form thegate wirings 502 and 503 including the gate electrodes, the capacitorwiring 504 and the terminal 501 of the terminal portion, using alow-resistance conductive material. Therefore, aluminum (Al), copper(Cu), silver (Ag), gold (Au), platinum (Pt) or the like, or an alloycontaining the above element as a constituent, can be used as amaterial. However, since aluminum (Al), copper (Cu) and silver (Ag) aredisadvantageous in their low thermal resistance, high corrosiveness andthe like, these elements can be used in combination with a thermallyresistant conductive material.

[0139] Next, an insulating film 506 is formed on the entire surface. Asilicon nitride film is used as the insulating film 506, and is formedto have a thickness of 50 to 200 nm, preferably, 150 nm. Note that thegate insulating film 506 is not limited to the silicon nitride film; aninsulating film such as a silicon oxide film, a silicon nitride oxidefilm or a tantalum oxide film can also be used (FIG. 5B).

[0140] Next, an amorphous semiconductor film 505 with a thickness of 50to 200 nm, preferably, 100 to 150 nm, is formed on the entire surface ofthe insulating film 506 through a known method such as a plasma CVDmethod or a sputtering method. Typically, an amorphous silicon (a-Si)film is formed to have a thickness of 100 nm (FIG. 5B).

[0141] Then, a second photolithography step is conducted to form aresist mask 507. An unnecessary portion is removed by etching to form anamorphous semiconductor film 508. In Embodiment 2, the amorphoussemiconductor film 508 is formed by dry etching using a mixed gas ofCl₂=40 sccm and BCl₃=40 sccm as an etching gas. As a result of etching,the ends of the amorphous semiconductor film 508 are tapered at an anglein the range of 5 to 45 degrees. Although the mixed gas of Cl₂=40 sccmand BCl₃=40 sccm is used as an etching gas in Embodiment 2, acomposition of the etching gas is not limited to the above-mentionedcomposition as long as a TFT with a shape shown in FIG. 5C is obtained;for example, a gas selected from the group consisting of Cl₂, BCl₃, HCland SiCl₄, or a mixed gas of a plurality of gases selected from theabove group can be used as an etching gas.

[0142] Next, after removal of the resist mask 507, another resist maskis formed by using a shadow mask. After the insulating film 506, whichcovers a pad portion of the terminal portion, is selectively removed toform an insulating film 601, the resist mask is removed (FIG. 6A).Instead of using the shadow mask, a resist mask formed by screenprinting may alternatively be used as an etching mask.

[0143] Next, a doping step is conducted to form an LDD (lightly dopeddrain) region of the n-channel TFT. The doping is performed by iondoping or ion implantation. Phosphorus is added as an n-type impurity soas to form impurity regions 604 to 606 with the use of second insulatingfilms 602 and 603 as masks. A donor density of these regions is set to1×10¹⁶ to 1×10¹⁷/cm³.

[0144] Then, a conductive film 608 of a transparent conductive film isformed on the entire surface (FIG. 6C). The conductive film 608 isformed by sputtering or vacuum evaporation, using indium oxide (In₂O₃)or an alloy of indium oxide and tin oxide (In₂O₃-SnO₂; abbreviated asITO) as a material. An etching treatment for such a material isconducted with a chlorine type solution.

[0145] Next, a third photolithography step is conducted to form a resistmask 701. An unnecessary portion is removed by etching to form a sourcewiring 706, a source region 702, a drain region 704 and a pixelelectrode 705 (FIG. 7B).

[0146] Subsequently, the resist mask 701 is removed. FIG. 7C shows across-sectional view in this state.

[0147] As described above, through three photolithography steps, a lighttransmitting semiconductor display device including the source wiring706, an inverse-stagger pixel TFT 707, a storage capacitor 708 and aterminal portion 709 can be manufactured.

[0148] As in Embodiment 1, a driving circuit formed with an IC chip ismounted to perform the image display in Embodiment 2.

Embodiment 3

[0149] Embodiment 3 of the present invention will be described withreference to FIGS. 8 to 10C. In Embodiment 3, a manufacturing method ofa liquid crystal display device is described. A method of manufacturingan inverse-stagger TFT in a pixel portion on a substrate andmanufacturing a storage capacitor connected to the TFT will be describedin detail in the order of the manufacturing steps. In FIGS. 9A to 10C, aterminal portion, which is provided at the end of the substrate so as tobe electrically connected to a wiring of a circuit provided on anothersubstrate, is also illustrated in the steps of manufacturing a TFT. Thecross-sectional views of FIGS. 9A to 10C correspond to the cross sectioncut along a line A-A′ in FIG. 8.

[0150] First, a semiconductor display device is manufactured by using asubstrate 1200 with light transmittance. As the substrate 1200, a glasssubstrate such as barium borosilicate glass and alumino borosilicateglass, as represented by #7059 glass and #1737 glass manufactured byCorning Inc., can be used. Besides, a light transmitting substrate suchas a quartz substrate and a plastic substrate can also be used as thesubstrate 1200.

[0151] After forming a conductive film on the entire surface of thesubstrate 1200, a first photolithography step is conducted to form aresist mask. An unnecessary portion is removed by etching so as to formgate electrodes 1202 and 1203, a storage capacitor wiring 1204, and aterminal portion 1201 (FIG. 9A).

[0152] As a material for the electrodes 1202 and 1203, an elementselected from the group consisting of titanium (Ti), tantalum (Ta),tungsten (W), molybdenum (Mo), chromium (Cr) and neodymium (Nd), analloy containing the above element as a constituent, or a nitridecontaining the above element as a constituent, is used. Alternatively,the combination of plural selected from: an element selected from thegroup consisting of titanium (Ti), tantalum (Ta), tungsten (W),molybdenum (Mo), chromium (Cr) and neodymium (Nd); an alloy containingthe above element as a constituent; and a nitride containing the aboveelement, can be deposited as a laminate layer to form the electrodes1202 and 1203.

[0153] For application to a large screen, it is desirable to form gatewirings including the gate electrodes 1202 and 1203, the capacitorwiring 1204 and a terminal of the terminal portion 1201, using alow-resistance conductive material. Therefore, aluminum (Al), copper(Cu), silver (Ag), gold (Au), platinum (Pt) or the like or an alloycontaining the above element as a constituent can be used as a material.However, since aluminum (Al), copper (Cu) and silver (Ag) aredisadvantageous in their low thermal resistance, high corrosiveness andthe like, these elements can be used in combination with a thermallyresistant conductive material.

[0154] Next, an insulating film 1207 is formed on the entire surface. Asilicon nitride film is used as the insulating film 1207, and is formedto have a thickness of 50 to 200 nm, preferably, 150 nm. The gateinsulating film 1207 is not limited to the silicon nitride film; aninsulating film such as a silicon oxide film, a silicon nitride oxidefilm or a tantalum oxide film can also be used (FIG. 9B).

[0155] Next, a first amorphous semiconductor film 1206 with a thicknessof 50 to 200 nm, preferably, 100 to 150 nm, is formed on the entiresurface of the insulating film 1207 through a known method such as aplasma CVD method or a sputtering method. Typically, an amorphoussilicon (a-Si) film is formed to have a thickness of 100 nm. As thefirst amorphous semiconductor film 1206, a microcrystallinesemiconductor film and a compound semiconductor film with an amorphousstructure, such as an amorphous silicon germanium film, or an amorphoussilicon carbide film can also be used (FIG. 9B).

[0156] Next, a second amorphous semiconductor film 1205 containing animpurity element with one conductivity type (n-type or p-type) is formedto have a thickness of 50 to 200 nm. The second semiconductor film 1205containing an impurity element with one conductivity type (n-type orp-type) is formed on the entire surface by a known method such as aplasma CVD method or a sputtering method. In Embodiment 3, the secondamorphous semiconductor film 1205 containing an n-type impurity elementis formed by using a silicon target to which phosphorus (P) is added.Alternatively, the second amorphous semiconductor film 1205 may beformed with a silicon target by sputtering in an atmosphere containingphosphorus. Further alternatively, the second amorphous semiconductorfilm 1205 containing an impurity element that imparts an n-typeconductivity may be formed of a microcrystalline silicon hydride film(FIG. 9B). Further, a conductive film 1205 b comprising metallicmaterial is formed to a thickness of 50 to 200 nm by sputtering or thelike. (FIG. 9(B))

[0157] Then, a second photolithography step is conducted to form aresist mask 1208. A conductive film and a first amorphous semiconductorfilm 1209 and a second amorphous semiconductor film 1210 containing animpurity element with one conductivity type (n-type or p-type) areformed to have a desired shape by etching. In Embodiment 3, the firstamorphous semiconductor film 1209 and the second amorphous semiconductorfilm 1210 containing an impurity element with one conductivity type(n-type or p-type) and the conductive film 1210 b are formed by dryetching using a mixed gas of Cl₂=40 sccm and BCl₃=40 sccm as an etchinggas. As a result of etching, the ends of the conductive film 1210 b andthe second amorphous semiconductor film 1210 containing an impurityelement with one conductivity type (n-type or p-type) are formedperpendicular to the substrate, whereas the ends of the first amorphoussemiconductor film 1209 are tapered at an angle in the range of 5 to 45degrees (FIG. 9C).

[0158] The ends of the second amorphous semiconductor film 1210containing an impurity element with one conductivity type (n-type orp-type) may also be tapered. Although the mixed gas of Cl₂=40 sccm andBCl₃=40 sccm is used as an etching gas in Embodiment 3, a composition ofan etching gas is not limited to the above-mentioned composition as longas a TFT with a shape shown in FIG. 9C is obtained; for example, a gasselected from the group consisting of Cl₂, BCl₃, HCl and SiCl₄ or amixed gas of a plurality of gases selected from the above group can beused as an etching gas.

[0159] Next, with continuous use of the resist mask 1208, an insulatingfilm 1211 is formed in a desired shape by etching. In Embodiment 3, theinsulating film 1211 is formed by dry etching using a gas of CHF₃=35sccm as an etching gas (FIG. 9C). Although a gas of CHF₃=35 sccm is usedas an etching gas in Embodiment 3, a composition of the etching gas isnot limited thereto as long as a TFT with a shape shown in FIG. 9C ismanufactured.

[0160] Then, a conductive film 1301 of a transparent conductive film isformed on the entire surface (FIG. 10A). The conductive film 1301 isformed by sputtering, vacuum evaporation, or the like using indium oxide(In₂O₃) or an alloy of indium oxide, tin oxide (In₂O₃-SnO₂; abbreviatedas ITO) etc., as a material.

[0161] Next, a third photolithography step is conducted to form a resistmask 1302. An unnecessary portion is removed by etching to form a sourcewiring 1303, a source region, a drain region, a drain electrode 1305 anda pixel electrode 1306 (FIG. 10B). It is to be noted that after theconductive film comprising a transparent conductive film is subjected toen etching treatment using a chlorine type solution, the metal film andthe second amorphous semiconductor film are etched by using a gas.Further, in the above third photolithography step, in order tocompletely separate the source region and the drain region from eachother, an overetching is conducted, and a part of the first amorphoussemiconductor film is removed.

[0162] Subsequently, the resist mask 1302 is removed. FIG. 10C shows across-sectional view in this state.

[0163] As described above, through three photolithography steps, anactive matrix substrate including the source wiring 1303, aninverse-stagger pixel TFT 1308, a storage capacitor 1309 and a terminalportion 1310 can be manufactured. With respect to the following steps,by using known technique, formation of orientation film and rubbingtreatment and sticking of counter substrate and injection of liquidcrystal and sealing and sticking of FPC are conducted to complete atransmission type liquid crystal display device.

[0164] Further, if necessary, a protective film comprising siliconnitride film and silicon oxynitride film may be formed. It is notprovided over a terminal electrode connected with FPC or the like.

[0165] The TFT including an active layer formed of the amorphoussemiconductor film, obtained in Embodiment 3, has a small field-effectmobility, i.e., only about 1 cm²/Vsec. Therefore, a driving circuit forperforming the image display is formed with an IC chip, and is mountedthrough TAB (tape automated bonding) or COG (chip on glass).

[0166] Further, a TFT having a multi-gate structure comprising aplurality of channel formation regions, here a TFT having a double gatestructure, is illustrated in Embodiment 3. However, a single gatestructure may be used without limitation.

Embodiment 4

[0167] The semiconductor display device including the channel etch typeTFT in the pixel portion has been described in Embodiment 3, while asemiconductor display device including a channel stop type TFT in thepixel portion will be described in Embodiment 4 with reference to FIGS.11A to 13B.

[0168] First, a semiconductor display device is manufactured by using asubstrate 1400 with light transmittance. As the substrate 1400, a glasssubstrate such as barium borosilicate glass and alumino borosilicateglass, as represented by #7059 glass and #1737 glass manufactured byCorning Inc., can be used. Besides, a light transmitting substrate suchas a quartz substrate and a plastic substrate can also be used as thesubstrate 1400.

[0169] After forming a conductive film on the entire surface of thesubstrate 1400, a first photolithography step is conducted to form aresist mask. An unnecessary portion is removed by etching to form gateelectrodes 1402 and 1403, a storage capacitor wiring 1404, and aterminal portion 1401 (FIG. 11A).

[0170] As a material for the electrodes 1402 and 1403, an elementselected from the group consisting of titanium (Ti), tantalum (Ta),tungsten (W), molybdenum (Mo), chromium (Cr) and neodymium (Nd), analloy containing the above element as a constituent, or a nitridecontaining the above element as a constituent, is used. Alternatively,the combination of plural selected from: an element selected from thegroup consisting of titanium (Ti), tantalum (Ta), tungsten (W),molybdenum (Mo), chromium (Cr) and neodymium (Nd); an alloy containingthe above element as a constituent; and a nitride containing the aboveelement as a constituent, can be deposited as a laminate layer to formthe electrodes 1402 and 1403.

[0171] For application to a large screen, it is desirable to form gatewirings including the gate electrodes 1402 and 1403, the storagecapacitor 1404 and a terminal of the terminal portion 1401, using alow-resistance conductive material. Therefore, aluminum (Al), copper(Cu), silver (Ag), gold (Au), platinum (Pt) or the like, or an alloycontaining the above element as a constituent, can be used as amaterial. However, since aluminum (Al), copper (Cu) and silver (Ag) aredisadvantageous in their low thermal resistance, high corrosiveness andthe like, these elements can be used in combination with a thermallyresistant conductive material.

[0172] Next, an insulating film 1406 is formed on the entire surface. Asilicon nitride film is used as the insulating film 1406, and is formedto have a thickness of 50 to 200 nm, preferably, 150 nm. The gateinsulating film 1406 is not limited to the silicon nitride film; aninsulating film such as a silicon oxide film, a silicon nitride oxidefilm or a tantalum oxide film can also be used (FIG. 11B).

[0173] Next, an amorphous semiconductor film 1405 with a thickness of 50to 200 nm, preferably, 100 to 150 nm, is formed on the entire surface ofthe insulating film 1406 through a known method such as a plasma CVDmethod or a sputtering method. Typically, an amorphous silicon (a-Si)film is formed to have a thickness of 100 nm (FIG. 11B).

[0174] Then, a second photolithography step is conducted to form aresist mask 1407. An unnecessary portion is removed by etching to forman amorphous semiconductor film 1408. In Embodiment 4, the amorphoussemiconductor film 1408 is formed by dry etching using a mixed gas ofCl₂=40 sccm and BCl₃=40 sccm as an etching gas. As a result of etching,the ends of the amorphous semiconductor film 1408 are tapered at anangle in the range of 5 to 45 degrees. Although the mixed gas of Cl₂=40sccm and BCl₃=40 sccm is used as an etching gas in Embodiment 4, acomposition of an etching gas is not limited to the above-mentionedcomposition as long as a TFT with a shape shown in FIG. 11C is obtained;for example, a gas selected from the group consisting of Cl₂, BCl₃, HCland SiCl₄ or a mixed gas of a plurality of gases selected from the abovegroup can be used as an etching gas.

[0175] Next, with continuous use of the resist mask 1407, an insulatingfilm 1409 is formed in a desired shape by etching. In Embodiment 4, theinsulating film 1409 is formed by dry etching using a gas of CHF₃=35scem as an etching gas (FIG. 11C). Although a gas of CHF₃=35 sccm isused as an etching gas in Embodiment 4, a composition of the etching gasis not limited thereto as long as a TFT with a shape shown in FIG. 11Cis manufactured.

[0176] Next, a doping step is conducted to form an LDD (lightly dopeddrain) region of the n-channel TFT. The doping is performed by iondoping or ion implantation. Phosphorus is added as an n-type impurity soas to form impurity regions 1503 to 1505 with the use of secondinsulating films 1501 and 1502 as masks. A donor density of theseregions is set to 1×10¹⁶ to 1×10¹⁷/cm³ (FIG. 12A).

[0177] Then, a conductive film 1506 of a transparent conductive film isformed on the entire surface (FIG. 12B). The conductive film 1506 isformed by sputtering or vacuum evaporation, using indium oxide (In₂O₃)or an alloy of indium oxide and tin oxide (In₂O₃SnO₂; abbreviated asITO) as a material. An etching treatment for such a material isconducted with a chlorine type solution.

[0178] Next, a third photolithography step is conducted to form a resistmask 1601. An unnecessary portion is removed by etching to form a sourcewiring 1605, a source region 1602, a drain region 1604 and a pixelelectrode 1605 (FIG. 13A).

[0179] Subsequently, the resist mask 1601 is removed. FIG. 13B shows across-sectional view in this state.

[0180] As described above, through three photolithography steps, a lighttransmitting semiconductor display device including the source wiring1606, an inverse-stagger pixel TFT 1607, a storage capacitor 1608 and aterminal portion 1609 can be manufactured.

[0181] As in Embodiment 3, a driving circuit formed with an IC chip ismounted to perform the image display in Embodiment 4.

Embodiment 5

[0182] The active-matrix substrate and the liquid crystal displaydevice, manufactured through embodiments of the present invention, canbe used for various electro-optical apparatuses. Specifically, thepresent invention can be applicable for all electronic devices includingsuch an electro-optical apparatus as a display section.

[0183] As examples of such electronic devices, video cameras, carnavigation systems, personal computers and portable informationterminals (such as mobile computers, portable telephones, or electronicbooks) can be given. Some examples of these electronic devices are shownin FIGS. 14A to 14D.

[0184]FIG. 14A illustrates a personal computer including a main body801, an image input section 802, a display section 803 and a keyboard804.

[0185]FIG. 14B illustrates a video camera including a main body 805, adisplay section 806, a voice input section 807, operation switches 808,a battery 809 and an image-receiving section 810.

[0186]FIG. 14C is a digital camera including a main body 811, a camerasection 812, an image-receiving section 813, operation switches 814, anda display section 815.

[0187]FIG. 14D illustrates a player utilizing a recording mediumcontaining the recorded programs (hereinafter, simply referred to as arecording medium). This player includes a main body 816, a displaysection 817, a speaker section 818, a recording medium 819, andoperation switches 820. This device uses a DVD (Digital Versatile Disc),a CD or the like as a recording medium to allow the music, the movies,the games and the Internet to be enjoyed.

[0188] As described above, the present invention has an extremely wideapplication, and thus is applicable to electronic devices of variousfields. The electronic devices in Embodiment 5 can be realized with thestructure obtained by any combination of Embodiment mode 1, Embodimentmode 2 or any combination of Embodiments 1 to 4.

[0189] According to the present invention, the conductive film and thesecond amorphous semiconductor film and the first amorphoussemiconductor film can be removed with the same etching gas. Further, aTFT can be manufactured with three photomasks to realize improvement inproductivity and yield.

[0190] Moreover, the ends of the first amorphous semiconductor film aretapered in the present invention. As a result, the problems of poorcoverage of the pixel electrode can be solved.

What is claimed is:
 1. A semiconductor device comprising: a gate wiringformed over an insulating surface; an insulating film formed over thegate wiring; a first amorphous semiconductor film formed over theinsulating film; a source region and a drain region provided in a secondamorphous semiconductor film containing an impurity element of oneconductivity type, formed over the first amorphous semiconductor film;one of a source wiring and an electrode, provided on one of the sourceregion and the drain region; and a pixel electrode formed so as topartially overlap and be in contact with the electrode, wherein an endof the first amorphous semiconductor film has a tapered shape.
 2. Asemiconductor device comprising: a gate wiring formed over an insulatingsurface; an insulating film formed over the gate wiring; a firstamorphous semiconductor film provided over the insulating film; a sourceregion and a drain region provided in a second amorphous semiconductorfilm containing an impurity element of one conductivity type, providedover the first amorphous semiconductor film; one of a source wiring andan electrode, provided over one of the source region and the drainregion; and a pixel electrode provided so as to partially overlap and bein contact with the electrode, wherein one of an end of the firstamorphous semiconductor film and an end of the second amorphoussemiconductor film has a tapered shape.
 3. A semiconductor deviceaccording to claim 1 or claim 2 wherein the side edge of the firstamorphous semiconductor film having a tapered shape has an angle in therange of 5° to 45°.
 4. A semiconductor device comprising: a gate wiringformed over an insulating surface; a gate insulating film formed overthe gate wiring; an amorphous semiconductor film formed over the gateinsulating film; a source region and a drain region, formed over theamorphous semiconductor film; one of a source wiring and an electrode,formed over one of the source region and the drain region; and a pixelelectrode formed so as to partially overlap and be in contact with theelectrode, wherein a region overlapping with the gate wiring with thegate insulating film therebetween and not overlapping with the sourceregion or the drain region in the amorphous semiconductor film isthinner than other region and is tapered to become thinner toward acenter of the region.
 5. A semiconductor device according to claim 4wherein the region tapered has an angle in the range of 5° to 45°.
 6. Asemiconductor device according to claim 4 or claim 5 wherein the sideedge of the first amorphous semiconductor film has a taper shape with anangle in the range of 5° to 45°.
 7. A semiconductor device according toclaims 1 to 6 wherein a side face of one of the source region and thedrain region is aligned with one of the source wiring and the electrode.8. A method of manufacturing a semiconductor device, comprising: a firststep of forming a gate wiring over an insulating surface; a second stepof forming an insulating film covering the insulating surface and thegate wiring; a third step of forming a first amorphous semiconductorfilm over the insulating film; a fourth step of forming a secondamorphous semiconductor film containing an impurity element of oneconductivity type over the first amorphous semiconductor film; a fifthstep of forming a conductive film comprising metallic material over thesecond amorphous semiconductor film; and a sixth step of etching theconductive film and the first amorphous semiconductor film and thesecond amorphous semiconductor film to form a side edge of the firstamorphous semiconductor film into a taper shape; a seventh step offorming a transparent conductive film over the conductive film; and aneighth step of etching a part of the first amorphous semiconductor filmand the transparent conductive film and the conductive film and thesecond amorphous semiconductor film to expose a part of the firstamorphous semiconductor film and to form a pixel electrode from thetransparent conductive film and form a source wiring from the conductivefilm and form source region and drain region from the second amorphoussemiconductor film.
 9. A method of manufacturing a semiconductor device,comprising: a first step of forming a gate wiring over an insulatingsurface; a second step of forming an insulating film covering theinsulating surface and the gate wiring; a third step of forming a firstamorphous semiconductor film over the insulating film; a fourth step offorming a second amorphous semiconductor film containing an impurityelement of one conductivity type over the first amorphous semiconductorfilm; a fifth step of forming a conductive film comprising metallicmaterial over the second amorphous semiconductor film; a sixth step ofetching the insulating film and the first amorphous semiconductor filmand the second amorphous semiconductor film and the conductive film toform a side edge of the first amorphous semiconductor film into a tapershape; a seventh step of forming a transparent conductive film over theconductive film; and an eighth step of etching a part of the firstamorphous semiconductor film and the transparent conductive film and theconductive film and the second amorphous semiconductor film to expose apart of the first amorphous semiconductor film and to form a pixelelectrode from the transparent conductive film and form a source wiringfrom the conductive film and form a source region and a drain regionfrom the second amorphous semiconductor film.
 10. A method ofmanufacturing a semiconductor device according to claim 8 or claim 9wherein in the sixth step, the conductive film and the second amorphoussemiconductor film and the first amorphous semiconductor film are etchedwith a chlorine type gas.
 11. A method of manufacturing a semiconductordevice according to any one of claims 8 to 10 wherein in the eighthstep, a part of the first amorphous semiconductor film and theconductive film and the second amorphous semiconductor film are etchedwith a chlorine type gas.
 12. A method of manufacturing a semiconductordevice according to any one of claims 8 to 11 wherein the chlorine typegas is selected from Cl₂ and BCl₃, HCl and SiCl₄ or a gas containing aplurality of gases selected from these gases.
 13. A method ofmanufacturing a semiconductor device, comprising: a step of forming agate wiring over an insulating surface; a step of forming an insulatingfilm over the insulating surface and the gate wiring; a step of forminga first amorphous semiconductor film over the insulating film; a step offorming a second amorphous semiconductor film containing an impurityelement of one conductivity type over the first amorphous semiconductorfilm; a step of forming a conductive film over the second amorphoussemiconductor film; and a step of etching the conductive film and thefirst amorphous semiconductor film and the second amorphoussemiconductor film to form a side edge of the first amorphoussemiconductor film into a taper shape; a step of forming a transparentconductive film over the second amorphous semiconductor film; and a stepof etching the transparent conductive film and the conductive film andthe second amorphous semiconductor film to form a source wiring and asource region and a drain region, wherein the conductive film containsaluminum or titanium, and wherein the first amorphous semiconductor filmis etched into a taper shape with a mixture gas Cl₂ and BCl₂.
 14. Amethod of manufacturing a semiconductor device, comprising: a step offorming a gate wiring over an insulating surface; a step of forming aninsulating film over the insulating surface and the gate wiring; a stepof forming a first amorphous semiconductor film over the insulatingfilm; a step of forming a second amorphous semiconductor film containingan impurity element of one conductivity type over the first amorphoussemiconductor film; a step of forming a conductive film over the secondamorphous semiconductor film; a step of etching the first amorphoussemiconductor film and the second amorphous semiconductor film and theconductive film to form a side edge of the first amorphous semiconductorfilm into a taper shape; a step of forming a transparent conductive filmover the second amorphous semiconductor film; a step of etching thetransparent conductive film and the conductive film and the secondamorphous semiconductor film to form a source wiring and a source regionand a drain region, wherein the conductive film contains at leasttantalum, and wherein the first amorphous semiconductor film is etchedinto a taper shape with a mixture gas of Cl₂ and CF₄.
 15. A method ofmanufacturing a semiconductor device, comprising: a step of forming agate wiring over an insulating surface; a step of forming an insulatingfilm over the insulating surface and the gate wiring; a step of forminga first amorphous semiconductor film over the insulating film; a step offorming a second amorphous semiconductor film containing an impurityelement of one conductivity type over the first amorphous semiconductorfilm; a step of forming a conductive film over the second amorphoussemiconductor film; a step of etching the first amorphous semiconductorfilm and the second amorphous semiconductor film and the conductive filmto form a side edge of the first amorphous semiconductor film into ataper shape; a step of forming a transparent conductive film over thesecond amorphous semiconductor film; and a step of etching thetransparent conductive film and the conductive film and the secondamorphous semiconductor film by etching to form a source wiring and asource region and a drain region, wherein the conductive film containsat least tungsten, and wherein the first amorphous semiconductor film isetched into a taper shape with a mixture gas of Cl₂ and CF₄ and O₂ or amixture gas of Cl₂ and SF₆ and O₂.